Olefin-vinyl alcohol-vinyl acetal copolymers, process for preparation thereof and laminate structures including said copolymers

ABSTRACT

A copolymer comprising 10 to 50 mole % of olefin units and 90 to 50 mole % of vinyl units, 50 to 98 mole % of the vinyl units being vinyl alcohol units and 2 to 50 mole % of the vinyl units being vinyl acetal units, is disclosed. This copolymer has excellent resistance to hot water and excellent oxygen barrier property in combination. When this copolymer is subjected to retort-sterilization, blanching is not caused and the excellent oxygen barrier property can be maintained. When this copolymer is laminated on a polyolefin or the like, a laminate structure excellent in the interlaminar peel strength is provided.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

This invention relates to an olefin-vinyl alcohol-vinyl acetal copolymerhaving excellent resistance to hot water and excellent oxygen barrierproperty in combination and also to a process for the preparationthereof. Further, the invention relates to a packaging material composedof said olefin-vinyl alcohol-vinyl acetal copolymer. Still further, theinvention relates to a laminate structure having excellent resistance tohot water, excellent oxygen barrier property and high interlaminar peelstrength in combination and more particularly, the invention concerns alaminate structure including a layer consisting of a novel olefin-vinylalcohol-vinyl acetal copolymer.

(2) Description of the Prior Art

Ethylene-vinyl alcohols are ordinarily prepared by saponifying anethylene-vinyl acetate copolymer. Accordingly, they are called"saponified ethylene-vinyl acetate copolymers". These saponifiedcopolymers are broadly used as packaging materials for foods andmedicines, especially for formation of packaging vessels. Properties ofsuch saponified ethylene-vinyl acetate copolymers are changed dependingon the ethylene content, the degree of saponification, the intrinsicviscosity and other factors, but they are excellent in the oxygen gasbarrier property, the flavor-retaining property, the oil resistance andthe transparency irrespective of these factors. Accordingly, when a filmor other shaped article composed of such saponified copolymer is used asa structural material of a packaging vessel or as an oxygen barrierlayer of a laminate material for production of a multi-layer vessel,decomposition or discoloration of the content by oxygen can be preventedand also deterioration of the taste or flavor or dispersion of theflavor can be prevented. Still further, bleeding of an oil or the likein the content to the surface of the vessel is not caused. Accordingly,various advantages are attained by the use of such saponifiedcopolymers.

However, saponified ethylene-vinyl acetate copolymers are poor in theresistance to polar solvents such as water, and when they are exposed tohot water or steam as in the case of hot water sterilization or retortsterilization (heating sterilization under pressure) of foods, themechanical strength is drastically reduced and such undesirablephenomena as deformation and adhesion are caused in films or vesselscomprising these saponified copolymers, resulting in occurrence of suchdefects as blanching, wrinkling, contraction and interlaminar peeling.These defects are also observed even when such saponified ethylene-vinylacetate copolymer is used as an intermediate layer of a multi-layerlaminate structure including at least three layers so as to preventdirect contact of the copolymer with hot water or steam. Recently, inorder to retain the flavor, color and texture of a packaged food aftersterilization, there has been developed a so-called high-temperatureshort-time sterilization process (HTST process) in which sterilizationis conducted under heating for a short time at a temperature higher than130° C. Under such high-temperature retort sterilization conditions,even dissolution of saponified ethylene-vinyl acetate copolymers isobserved. Even sterilization using hot water maintained at a temperatureof 80° C. or higher is difficult in case of a film or vessel composed ofa saponified ethylene-vinyl acetate copolymer and even when thesaponified copolymer is used as an intermediate layer of a multi-layerlaminate structure, defects such as blanching and wrinkling are causedunder such high temperature conditions as adopted in retortsterilization and therefore, such laminate structure cannot practicallybe applied to the use where sterilization is required.

Accordingly, at the present, the application field of saponifiedethylene-vinyl acetate copolymer is limited in the range wheresterilization is not required, though they have various merits andadvantages as packaging materials.

Various proposals have heretofore been made to improve the resistance tohot water in saponified ethylene-vinyl acetate copolymers. Among theseproposals, a method comprising laminating an olefinic resin on both thesurfaces of a film of a saponified ethylene-vinyl acetate copolymer ismost frequently adopted in the art. A laminate structure obtainedaccording to this method has a resistance to water of a relatively lowtemperature, but it cannot resist the above-mentioned high-temperaturesterilization using hot water of a high temperature or steam.

Also various proposals have heretofore been made to improve the hotwater resistance by treating saponified ethylene-vinyl acetatecopolymers per se. For example, there can be mentioned a methodcomprising subjecting a film of the saponified copolymer to a treatmentwith hot water (see Japanese Patent Publication No. 13600/69), a methodcomprising dipping a film of the saponified copolymer in an aqueoussolution containing sulfuric acid or hydrochloric acid and thensubjecting the film to a treatment with hot water (see Japanese PatentPublication No. 114/71), a method comprising treating a shaped articleof the saponified copolymer with a solution of an organic titanate (seeJapanese Patent Publication No. 17071/71) and a method comprisingtreating a shaped article of the saponified copolymer with a solutioncomprising an alcohol, an organic carboxylic acid and an organictitanium compound (see Japanese Patent Publication No. 17915/71).However, according to these treatment methods, there are obtained onlyproducts which can resist the hot water treatment conducted at 100° C.at highest, and it is impossible to obtain products which can resist thehot water or steam treatment conducted at 120° C. or a highertemperature.

It has been known from old that when a film of a polyvinyl alcohol resinhaving an excellent oxygen gas barrier property is subjected to anacetalizing treatment using formaldehyde or the like, the hot waterresistance of the film can be improved. However, when a film of suchpolyvinyl alcohol resin is acetalized to such an extent that the filmcan resist the retort sterilization conducted at a temperature higherthan 120° C., the inherent oxygen gas barrier property of the film isdrastically degraded and no excellent packaging material is obtained.

BRIEF SUMMARY OF THE INVENTION

I found that a novel olefin-vinyl alcohol-vinyl acetal copolymercomprising olefin units, vinyl alcohol units and vinyl acetal units inspecific amounts has excellent oxygen barrier property and hot waterresistance in combination and is valuable as a heat-sterilizable sealingpackaging material.

It was also found that a laminate structure comprising the above novelcopolymer and a heat-sealable resin has a most desirable combination ofexcellent oxygen barrier property, high resistance to hot water and highinterlaminar peel strength and it can resist heat sterilization,especially heat sterilization conducted at a temperature higher than130° C.

I have now completed the present invention based on these findings.

It is a primary object of the present invention to provide a novelolefin-vinyl alcohol-vinyl acetal copolymer having a high oxygen barrierproperty (oxygen impermeability) comparable to that of an olefin-vinylalcohol copolymer, which can resist a hot water or hot steam treatmentconducted at a temperature higher than 120° C. and also to provide aprocess for the preparation of this novel copolymer.

Another object of the present invention is to provide a novel packagingresinous material which can be subjected to hot water sterilization,retort sterilization, high-temperature short-time sterilization and thelike treatments and which can preserve packaged foods for a long timeeven at room temperature.

Still another object of the present invention is to provide a laminatestructure comprising a layer of a novel olefin-vinyl alcohol-vinylacetal copolymer having a high oxygen barrier property (oxygenimpermeability) comparable to that of an olefin-vinyl alcohol copolymer,which can resist a hot water or hot steam streatment conducted at atemperature higher than 120° C.

A further object of the present invention is to provide a novelheat-sealable packaging laminate structure which can be subjected to hotwater sterilization, retort sterilization, high-temperature short-timesterilization and the like treatments and which can preserve packagedfoods for a long time even at room temperature.

In accordance with the present invention, there is provided anolefin-vinyl alcohol-vinyl acetal copolymer having excellent hot waterresistance and excellent oxygen barrier property in combination, whichconsists essentially of 10 to 50 mole % of olefin units and 90 to 50mole % of vinyl units, 50 to 98 mole % of the vinyl units being vinylalcohol units and 2 to 50 mole % of the vinyl units being at least onekind of vinyl acetal units selected from the group consisting of (A)units represented by the following formula: ##STR1## wherein R₁ standsfor a hydrogen atom or a monovalent aliphatic, aromatic oraliphatic-aromatic group,

(B) units represented by the following formula: ##STR2## wherein R₁ isas defined above, (C) units represented by the following formula:##STR3## wherein R₂ stands for a direct bond or a divalent aliphatic,aromatic or aliphatic-aromatic group, and (D) units represented by thefollowing formula: ##STR4## wherein R₂ is as defined above.

In accordance with the present invention, there is also provided alaminate structure having excellent hot water resistance, excellentoxygen barrier property and high interlaminar peel strength incombination, which comprises (i) a layer composed of the above-mentionednovel olefin-vinyl alcohol-vinyl acetal copolymer and (ii) a layercomposed of a heat-sealable resin.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a sectional view of a laminate structure of the presentinvention having two layers.

FIG. 2 is a sectional view of a laminate structure of the presentinvention having three layers.

FIG. 3-(A) is a sectional view showing an example of a four-layerlaminate structure of the present invention.

FIG. 3-(B) is a sectional view showing another example of a four-layerlaminate structure of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Copolymer

In the novel copolymer of the present invention, in order to attaindesirable combination of excellent oxygen gas barrier property and highhot water resistance, it is important that the content of olefin unitsshould be 10 to 50 mole %, especially 20 to 40 mole %, and the contentof vinyl units, namely the total content of vinyl alcohol units andvinyl acetal units, should be 90 to 50 mole %, especially 80 to 60 mole%. More specifically, if the content of the olefin units exceeds 50 mole% of the total units, the oxygen gas barrier property of the resultingcopolymer is much lower than that of the copolymer included in the scopeof the present invention, and the intended objects of the presentinvention cannot be attained by such copolymer. If the content of theethylene units in the copolymer is lower than 10 mole %, the hydrophilicproperty of the copolymer is enhanced and it is very difficult to attainhigh hot water resistance and excellent oxygen gas barrier property incombination, however diversely the ratio of the vinyl alcohol units andvinyl acetal units, described hereinafter, may be changed.

In the novel copolymer of the present invention, in order to attaindesirable combination of excellent oxygen gas barrier property and highhot water resistance, it is also important that 50 to 98 mole %,especially 70 to 95 mole %, of the vinyl units should be occupied byvinyl alcohol units and 2 to 50 mole %, especially 5 to 30 mole %, ofthe vinyl units should be occupied by at least one kind of vinyl acetalunits represented by the above-mentioned formulae (A) to (D). As willreadily be understood from experimental results shown in ComparativeExamples 1, 2 and 5 given hereinafter, in case of a copolymer having avinyl acetal unit content lower than 2 mole % of the total vinyl units,a satisfactory oxygen gas barrier property is attained, but a filmcomposed of this copolymer is readily whitened when contacted with hotwater maintained at 100° C. and the film tends to be dissolved whencontacted with hot water maintained at 135° C. In contrast, as will beapparent from experimental data shown in Comparative Examples 3 and 4given hereinafter, if the vinyl acetal unit content is higher than 50mole % of the total vinyl units, a satisfactory hot water resistance canbe attained, but the oxygen permeability becomes 50 times or higher andthe mechanical properties of the film, such as the strress-rupturestrength, are degraded. On the other hand, when the molar ratio of thevinyl alcohol units and vinyl acetal units is adjusted within theabovementioned range according to the present invention, the resistanceto hot water maintained at a temperature higher than 100° C., especiallyhigher than 130° C., can be remarkably improved while the oxygenimpermeability and mechanical properties are maintained at thesubstantially same levels as those of ethylene-vinyl alcohol copolymers.

The above effect attained by the present invention is quite surprising.For example, as shown in Table 1 given hereinafter, the oxygen gaspermeability of an ethylene-vinyl alcohol copolymer free of vinyl acetalunits is only 1.2 cc/m² per 24 hours, whereas the oxygen gaspermeability of a copolymer in which 56.4 mole % of the vinyl units ofthe above ethylene-vinyl alcohol copolymer are acetalized by glyoxal isas high as 52 cc/m² per 24 hours. Therefore, it is construed that theoxygen gas permeability of the above copolymer is enhanced with decreaseof the content of the vinyl alcohol units. Accordingly, in a copolymerhaving 7.1 mole % of the vinyl alcohol units acetalized, it is presumedthat the oxygen gas permeability may be equal to the arithmetic meancalculated from the above two values, namely 7.6 cc/m² per 24 hours. Asis shown in Example 4 given hereinafter, however, the above copolymer ofthe present invention has an oxygen gas permeability of only 1.5 cc/m²per 24 hours, which value is less than 1/5 of the arithmetic mean. Thisfact is quite surprising and cannot be expected from the abovepresumption at all.

In the copolymer of the present invention, any of olefins represented bythe following formula (A): ##STR5## wherein R₃ stands for a hydrogenatom or an alkyl group having up to 4 carbon atoms, can be used. Morespecifically, there can be used ethylene, propylene, butene-1,pentene-1, 4-methylpentene-1 and the like. These olefins may be usedsingly or in the form of a mixture of two or more of them.

Ethylene is most preferred among these olefins. Of course, an olefinother than ethylene, for example, propylene, may be used in combinationwith ethylene in an amount of up to 15 mole %, especially up to 10 mole%, of ethylene units.

The presence of units derived from the abovementioned olefin isindispensable for improving both the oxygen gas barrier property and hotwater resistance simultaneously in the copolymer of the presentinvention. The intended improvement cannot be attained at all in acopolymer free of olefin units. More specifically, as will readily beunderstood from experimental results shown in Comparative Examples 6 and7 given hereinafter, when a polyvinyl alcohol free of olefin units isacetalized within a range not causing substantial degradation of theoxygen gas barrier property (degree of acetalization=22.3 mole %), theacetalized polymer is whitened or dissolved when contacted with hotwater maintained at 100° C. and no satisfactory hot water resistance canbe attained. On the other hand, when the polyvinyl alcohol is acetalizedwithin a range providing a sufficient hot water resistance (degree ofacetalization=60.2 mole %), the oxygen permeability is abruptly enhancedto such a high level as 63.0 cc/m² per 24 hours.

PREPARATION OF COPOLYMER

In general, the olefin-vinyl alcohol-vinyl acetal copolymer is preparedby a process comprising reacting an olefin-vinyl alcohol copolymercomprising 10 to 50 mole % of olefin units and 90 to 50 mole % of vinylalcohol units with at least one member selected from the groupconsisting of monoaldehydes represented by the following formula (F):

    R.sub.1 --CHO

wherein R₁ stands for a hydrogen atom or a monovalent aliphatic,aromatic or aliphatic-aromatic group, and dialdehydes represented by thefollowing general formula (G):

    OHC--R.sub.2 --CHO

wherein R₂ stands for a direct bond or a divalent aliphatic, aromatic oraliphatic-aromatic group, thereby to acetalize 2 to 50 mole % ofhydroxyl groups in said olefin-vinyl alcohol copolymer.

As the starting olefin-vinyl alcohol copolymer, there can be used any ofcopolymers comprising units of at least one olefin selected from theabove-mentioned olefins and units of vinyl alcohol. These olefin-vinylalcohol copolymers are ordinarily prepared by saponifying a copolymer ofan olefin such as ethylene with a vinyl ester such as vinyl acetateaccording to known means so that the degree of saponification is atleast 90%, preferably at least 95%, especially preferably at least 98%.

The molecular weight of the olefin-vinyl alcohol copolymer that is usedin the present invention is not particularly critical, so far as thecopolymer has a film-forming molecular weight. In general, the viscosityof an olefin-vinyl alcohol copolymer is determined by using a mixedsolvent comprising 85% by weight of phenol and 15% by weight of water.In order to attain the objects of the present invention, it is preferredto use an olefin-vinyl alcohol copolymer in which the intrinsicviscosity [η] as measured at 30° C. in the above-mentioned mixed solventis at least 0.05 l/g, especially in the range of from 0.07 to 0.17 l/g.When the intrinsic viscosity [η] is lower than 0.05 l/g, the mechanicalstrength is insufficient when the resulting copolymer is formed into ashaped article. When the intrinsic viscosity [η] is higher than 0.17l/g, the moldability is often degraded.

Acetalization of an olefin-vinyl alcohol copolymer can be accomplishedin a homogeneous system while dissolving the copolymer in a solvent suchas water together with an aldehyde and an acid catalyst, especially whenthe olefin content is low. Further, acetalization can be performed in aheterogeneous system while dipping a powder or pellet of the startingcopolymer or a shaped article of the starting copolymer, such as a film,a sheet, a tube, a bottle, a pouch or other vessel, in an acetalizingbath. The latter acetalizing method is preferred.

The olefin-vinyl alcohol copolymer may be shaped according to knownmeans. For example, the copolymer can be shaped by melting the copolymerand extruding the melt at a temperature of 180° to 300° C. Formation ofa film or the like can be performed according to a ordinary T-die methodor inflation film-forming method, and bottles or other vessels can beprepared by extruding the copolymer in the form of a parison by using adie of the cross-head type or spider type and blow-molding the parisonin a split mold. The so shaped olefin-vinyl alcohol may be subjected toa known heat treatment conducted, for example, at 120° to 160° C. for 5to 60 minutes or to a uniaxial or biaxial stretching treatment prior tothe acetalization reaction.

As suitable examples of the monoaldehyde represented by the formula (F),there can be mentioned formaldehyde, acetaldehyde, propionaldehyde,n-butyl aldehyde, isobutyl aldehyde, acrolein, crotonaldehyde andbenzaldehyde. Among these monoaldehydes, formaldehyde is especiallypreferred. As suitable examples of the dialdehyde represented by theformula (G), there can be mentioned glyoxal, malonaldehyde, succinicaldehyde, glutaraldehyde, maleic aldehyde and terephthalaldehyde. Amongthese dialdehydes, glyoxal is especially preferred.

These aldehydes may be used singly or in the form of a mixture of two ormore of them.

In the present invention, when acetalization is carried out by using amonoaldehyde represented by the formula (F), there are formed so-callednon-crosslinked vinyl acetal units (A) owing to intramolecularacetalization or so-called crosslinked vinyl acetal units (B) owing tointermolecular acetalization. When a dialdehyde of the formula (G) isused for the acetalization, there are formed so-called non-crosslinkedvinyl acetal units (C) owing to intramolecular acetalization orso-called crosslinked vinyl acetal units (D) owing to intermolecularacetalization.

Whether crosslinked vinyl acetal units or non-crosslinked vinyl acetalunits are formed is remarkably influenced by such factors as the kind ofthe aldehyde to be used, the kind of the starting olefin-vinyl alcoholcopolymer and acetalization conditions. However, it may be said thatwhen a monoaldehyde is employed, in general, vinyl acetal units composedmainly of non-crosslinked units are formed, and that when a dialdehydeis employed, vinyl acetal units comprising crosslinked units andnon-crosslinked units at optional ratios may be prepared.

A copolymer comprising vinyl acetal units (C) and (D), which is formedby carrying out the acetalization by using a dialdehyde represented bythe formula (G), is especially preferred for attaining the intendedobjects of the present invention. More specifically, in case of acopolymer comprising both the acetal units (C) and (D), an especiallyhigh hot water resistance can be obtained by introduction of such asmall amount of the vinyl acetal units as 2 to 10 mole % based on thetotal vinyl units, and there is attained an advantage that reduction ofthe oxygen barrier property by introduction of the acetal units can bemaintained at a very low level. In this preferred copolymer, it ispreferred that the crosslinked vinyl acetal units (D) be present in anamount of at least 1 mole % based on the sum of the vinyl alcohol unitsand vinyl acetal units and that the molar ratio of non-crosslinked vinylacetal units (C)/crosslinked vinyl acetal units (D) be in the range offrom 1/0.3 to 1/50, especially from 1/0.5 to 1/30.

The acetalization of the olefin-vinyl alcohol copolymer may be carriedout according to any optional known means so far as the aboverequirements are satisfied. For example, the acetalization can beaccomplished by dipping a shaped article of an olefin-vinyl alcoholcopolymer in an acetalizing bath formed by dissolving an aldehyde and,if necessary, a catalyst or the like into an appropriate solvent.

Water is most preferred as the solvent. In addition, there may beemployed alcohols such as methanol and ethanol, organic acids such asacetic acid and ethers such as tetrahydrofuran and dioxane, and mixturesof these organic polar solvents, especially mixtures of these organicpolar solvents with water.

The acetalization rate is not particularly influenced by the aldehydeconcentration in the bath. When the aldehyde concentration is too low,however, all the aldehyde in the bath is completely consumed while thereaction advances. Further, even if the aldehyde concentration isespecially heightened, no particular effect or advantage can beattained. Therefore, it is ordinarily preferred that the aldehydeconcentration in the acetalizing bath be 1 to 15% by weight, especially3 to 10% by weight.

An acid catalyst is generally used as the catalyst for promoting theacetalization reaction, and inorganic acids such as sulfuric acid andhydrochloric acid are especially effective. The acid concentration inthe acetalizing bath has significant influences on not only the reactionspeed but also the degree of acetalization in the resulting copolymer.In the present invention, good results are obtained when theabove-mentioned acid catalyst is used at a concentration of b 5 to 50%by weight, especially 10 to 30% by weight.

When acetalization is conducted on a shaped article of an olefin-vinylalcohol copolymer, a water-soluble inorganic salt such as sodium sulfate(Glauber salt) can be added to the acetalizing bath so as to preventswelling of the shaped article, and in this case, the salt concentrationin the acetalizing bath is adjusted to 5 to 20% by weight.

The temperature and time required for the acetalization reaction areappropriately decided based on experiments so that the desired degree ofacetalization can be attained. In general, it is preferred that thereaction be carried out at a temperature of 0° to 250° C., especially30° to 90° C. The time necessary for the reaction is varied depending onthe composition of the acetalizing bath and the reaction temperature,but it is ordinarily preferred that the reaction be conducted for 1 to120 minutes, especially 5 to 60 minutes.

The acetalized copolymer may be washed with water and dried according toneed, and it may be subjected to a post treatment such as a heattreatment. Thus, the intended product is obtained.

In the present invention, the intended olefin-vinyl alcohol-vinyl acetalcopolymer is obtained according to the above-mentioned process. Thecontent of the vinyl acetal units in the so formed copolymer can bedetermined according to the method for measuring the degree ofacetalization, which will be described hereinafter. The fact that thecopolymer of the present invention includes any of the foregoing vinylacetal units (A) to (D) is confirmed by the infrared absorption spectrumanalysis. More specifically, in the infrared absorption spectrum of thecopolymer of the present invention, there is observed a characteristicinfrared absorption peak inherent of stretching vibrations of an acetalring of the formula --O--CH(R₁)--O-- or --O--CH(R₂)--O-- at a wavenumber of 1000-1030 cm⁻¹.

Since the copolymer of the present invention has the above-mentionedspecific absorption peak inherent of the above acetal ring, the infraredabsorbance ratio (R), determined according to the method describedhereinafter, of the copolymer of the present invention is 2.00 to 7.00,especially 2.30 to 6.00, when the monoaldehyde is used for theacetalization, and 1.20 to 2.50, especially 1.30 to 2.00, when thedialdehyde is used for the acetalization.

USES

The novel copolymer not only can resist hot water or steam maintained ata temperature higher than 100° C., especially higher than 120° C., butalso has an excellent oxygen barrier property comparable to that of anuntreated ethylene-vinyl alcohol copolymer. Accordingly, the copolymerof the present invention is especially valuable as a packaging materialfor preserving a food or the like under sealing after heat sterilizationconducted according to need.

For example, the copolymer of the present invention can beadvantageously used as a sealing film container such as a pouch in theform of a single film or a laminate film formed by laminating a film ofthe copolymer of the present invention on a film of other syntheticresin, a metal foil or a paper for packaging a food, a medicine, acosmetic material or the like.

A sheet or thick film composed of the copolymer of the present inventionor a laminate including the copolymer of the present invention may bemolded according to known plastic processing means such as vacuummolding, air-pressure forming, sheet blow molding, draw forming,draw-ironing forming, compression molding, forward extrusion, backwardextrusion, forward-backward extrusion and explosion forming, and it maybe advantageously used in the form of a cup or other seamless bottomedvessel.

Still further, a parison composed of the copolymer of the presentinvention or a laminate including the copolymer of the present inventionmay be blow-molded or draw-blow-molded according to known means, and thecopolymer of the present invention may be advantageously used as apackaging vessel in the form of a hollow bottle, a tank or a tube.

LAMINATE STRUCTURE

In accordance with one of most important embodiments of the presentinvention, there is obtained a laminate structure having excellent hotwater resistance, excellent oxygen gas barrier property and highinterlaminar peel strength in combination by laminating theabove-mentioned olefin-vinyl alcohol-vinyl acetal copolymer with aheat-sealable resin. The fact that this desirable combination of theabove-mentioned three properties can be obtained only when the copolymerof the present invention is used will readily be understood fromexperimental data shown in Table 2 given hereinafter.

The laminate structure of the present invention may have an optionallayer arrangement, for example, a two-layer arrangement, a three-layerarrangement or a multi-layer arrangement of four or more layers, so faras it includes (i) a layer of the above-mentioned olefin-vinylalcohol-vinyl acetal copolymer (often referred to as "vinyl acetalcopolymer") and (ii) a heat-sealable resin.

For example, the laminate structure of the present invention may be atwo-layer structure including a layer 1 composed of the vinyl acetalcopolymer and a layer 2 composed of the heat-sealable resin as shown inFIG. 1.

Further, the laminate structure of the present invention may be athree-layer structure including, as shown in FIG. 2, an intermediatelayer 1 composed of the vinyl acetal copolymer, a first outer layer 2 ofthe heat-sealable resin disposed on one side of the intermediate layer 1and a second outer layer 3 of a heat-resistant resin disposed on theother side of the intermediate layer 1.

Still further, if desired, the laminate structure of the presentinvention may be a four-layer structure including, as shown in FIG.3-(A), the above-mentioned three layers shown in FIG. 2 and other resinlayer 4a, for example, a shock-absorbing layer interposed between thevinyl acetal copolymer layer 1 and the heat-sealable resin layer 2.Alternately, the laminate structure of the present invention may be afour-layer structure including, as shown in FIG. 3-(B), theabove-mentioned three layers shown in FIG. 2 and other layer 4b, forexample, a shock-absorbing layer or printing ink barrier layerinterposed between the vinyl acetal copolymer layer 1 and theheat-resistant resin layer 3.

In each case, the respective resin layers may be bonded together throughan adhesive layer (not shown) described hereinafter or they may bebonded directly without using an adhesive layer by fusion bonding underheating or similar means.

In the present invention, in order to impart the heat sealability to thefinal laminate structure, it is important to use a heat-sealable resinlayer in combination with a layer of the above-mentioned vinyl acetalcopolymer.

Any of resins that can be molten and become sealable under heating canbe used as the heat-sealable resin in the present invention. Forexample, there can be used polyolefins such as low density polyethylene,medium density polyethylene, high density polyethylene, polypropylene,polybutene-1, poly-4-methylpentene-1, ethylene-vinyl acetate copolymersand mixtures thereof, polyamides such as nylon-11 and nylon-12, andpolyesterethers.

A suitable heat-sealable resin is selected among these polymers,especially polyolefins, according to the heat sterilization treatmentconditions to be adopted. For example, when the final product issubjected to a heat sterilization treatment conducted at a temperaturelower than 130° C., medium density or high density polyethylene can beused, and when the heat sterilization treatment is carried out at atemperature lower than 100° C., low density polyethylene can be used.Further, when the heat sterilization treatment is conducted at a hightemperature of at least 130° C., an unstretched polypropylene film (casepolypropylene film) or a film of poly-4-methylpentene-1 can beadvantageously used. Still further, modified polypropylene obtained byblock-, random- or graft-copolymerizing propylene with other olefin suchas ethylene or butene-1 in an amount of up to 15 mole % based onpropylene and a blend of polypropylene with other polyolefin such ashigh density polyethylene in an amount of up to 10% by weight can beused so far as the steric regularity of polypropylene is not lost.

When the openability by peeling is required for the heat-sealedinterface of the laminate structure, it is possible to incorporate intothe above-mentioned crystalline polyolefin 2 to 30% by weight of anelastomer such as an ethylene-propylene rubber, anethylene-propylene-non-conjugated diene rubber, a styrenebutadienerubber, a butadiene rubber, polyisoprene or a butyl rubber according tothe know recipe.

In case of a three-layer laminate structure as shown in FIG. 2, as theheat-resistant resin layer, there is employed a layer of an optionalresin having a melting or softening point higher than that of theheat-sealable resin. For example, there are preferably employedpolyesters, polycarbonates and cellulose esters.

As the polyester, there can be used polyesters consisting of recurringunits represented by the following formula: ##STR6## wherein R₄ standsfor an alkylene or cycloalkylene group having 2 to 8 carbon atoms and R₅stands for an alkylene or arylene group having 2 to 24 carbon atoms. Forexample, there are employed polyethylene adipate, polyethylene sebacate,polyethylene terephthalate, polytetramethylene isophthalate,polyethylene terephthalate/isophthalate andpoly-1,4-cyclohexylenedimethylene terephthalate.

As the polycarbonate, there can be used polycarbonates having recurringunits represented by the following formula: ##STR7## wherein R₆ standsfor a hydrocarbon group having 8 to 15 carbon atoms. For example, therecan be used poly-p-xylene-glycol biscarbonate,polydihydroxydiphenylmethane carbonate, polydihydroxyphenylethanecarbonate, polydihydroxydiphenyl-2,2-propane carbonate andpolydihydroxydiphenyl-1,1-ethane carbonate.

As the cellulose ester, there can be used various acetyl cellulosesdiffering in the degree of acetylation.

When a polyolefin is used as the heat-sealable resin, as theheat-resistant resin there can be used polyamides having a melting pointhigher than the melting point of the polyolefin, especially polyamidesconsisting of recurring units represented by the following formula:##STR8## wherein n is a number of from 3 to 13 and m is a number of from4 to 11. For example, there can be used poly-ω-aminocaproic acid,poly-ω-aminoheptanoic acid, poly-ω-aminocaprylic acid,poly-ω-aminopelargonic acid, poly-ω-aminoundecanoic acid,poly-ω-aminododecanoic acid, poly-ω-aminotridecanoic acid,polyhexamethylene adipamide, polyhexamethylene sebacamide,polyhexamethylene dodecamide, polyhexamethylene tridecamide,polydecamethylene adipamide, polydecamethylenesebacamide,polydecamethylene dodecamide, polydecamethylene tridecamide,polydodecamethylene adipamide, polydodecamethylene sebacamide,polydodecamethylene dodecamide, polydodecamethylene tridecamide,polytridecamethylene adipamide, polytridecamethylene sebacamide,polytridecamethylene dodecamide, polytridecamethylene tridecamide,polyhexamethylene azelamide, polydecamethylene azelamide,polydodecamethylene azelamide and polytridecamethylene azelamide.

Furthermore, when polyethylene is used as the heat-sealable resin, abiaxially stretched polypropylene film can be used as the heat-resistantresin layer.

As the shock-absorbing layer that is used for a laminate structureincluding 4 or more layers as shown in FIG. 3-(A) or 3-(B), there isemployed a film of a resin having a shock absorption coefficient K_(I)of at least 0.5×10⁻⁴ cm, especially at least 1.0×10⁻⁴ cm, as determinedaccording to the method described below.

The shock absorption coefficient referred to in the instantspecification is determined according to the following method.

A sample resin film is subjected to the retort treatment at 135° C. for10 minutes, and the retorted sample is pulled at a rate of 200 m/min inboth the machine direction and a direction rectangular thereto at roomtemperature. The load S under 30% stretching of the sample film isdetermined in the unit of Kg/cm of the film width. Then, the filmretorted under the same conditions as described above is pulled at thesame temperature and pulling speed in the same directions as describedabove, and the tensile modulus E (in the unit of Kg/cm²) is determined.With respect to each of the machine direction and the directionrectangular thereto, the tensile load (S) is divided by the tensilemodulus (E). Of the so obtained two values, the smaller value is definedas the shock absorption coefficient (K_(I), the unit being cm).

When polypropylene or poly-4-methylpentene-1 is used as theheat-sealable resin, this shock absorbing layer is especially valuableand effective for improving the resistance to falling shock and othermechanical properties of a packaged container which has been subjectedto the retort sterilization. A resin having a K_(I) value in theabove-mentioned range is selected from the above-mentioned polyamides,polycarbonates and polyesters and is used as the shock absorbinglayer-constituting resin. A preferred shock absorbing layer is apolyamide film, especially a biaxially stretched film ofpolycaprolactam. Still further, as the shock absorbinglayer-constituting resin there may be used polyester-ethers, especiallythose consisting of recurring units represented by the followingformula:

    {[OOC-R.sub.7 -COO(CH.sub.2).sub.n ].sub.p OOC(R.sub.7 -CO-**-[O(CH.sub.2).sub.m ].sub.l).sub.q }                (M)

wherein R₇ stands for a phenylene group, n is a number of from 2 to 4, mis a number of from 2 to 5, l is a number of at least 2, preferably anumber of from 6 to 10, and each of p and q is a number of at least 2.

As examples of the polyester-ether having the above recurring units,there can be mentioned polyoxyethyleneethylene terephthalate,poly-1,4-oxybutylene-1,4-butylene terephthalate, andpoly-1,4-oxybutylene-ethylene terephthalate.

As the resin constituting a printing ink barrier layer in the laminatestructure as shown in FIG. 3-(A) or 3-(B), there may be used, forexample, polyamides and polyesters.

In formation of the laminate structure of the present invention, theabove-mentioned vinyl acetal copolymer layer and heat-sealable resinlayer optionally with the heat-resistant resin layer, shock absorbinglayer and printing ink barrier layer may be laminated according to knownlaminating means such as dry lamination, extrusion coating, extrusionlamination and coextrusion.

For example, a film of the vinyl acetal copolymer and a film of theheat-sealable resin are prepared in advance, and they are bondedtogether by a known adhesive such as an isocyanate type adhesive, anepoxy type adhesive or an isocyanate-epoxy type adhesive to form alaminate structure. In case of a three-layer structure as shown in FIG.2, a film of the heat-resistant resin is bonded to the other side of thevinyl acetal copolymer film, namely on the side opposite to the side towhich the heat-sealable resin layer is bonded, according to theabove-mentioned bonding means. Further, a four-layer structure as shownin FIG. 3-(A) or 3-(B) may be formed by similar means.

A film of the vinyl acetal copolymer is prepared in advance, and theheat-sealable resin optionally with the heat-resistant resin is extrudedin the form of a layer on one or both of the surfaces of the film andfusion-bonded thereto to form a laminate structure. In this case, inorder to improve the bondability between the two resins, the surface ofthe vinyl acetal film may be treated in advance with an anchoring agentsuch as a titanic acid ester or an isocyanate compound according toknown procedures.

A film of the vinyl acetal copolymer and a film of the heat-resistantresin or heat-sealable resin are prepared in advance, and the shockabsorbing layer-constituting resin, which also acts as an adhesive, forexample, a polyamide or polyester-ether, is extruded between the tworesin films to bond the two films and form a laminate structure.

Still further, a laminate structure can be directly formed bycoextruding the vinyl acetal copolymer and heat-sealable resinoptionally with the heat-resistant resin through a multi-ply die.

In the laminate structure of the present invention, sufficient oxygenbarrier property is attained if the thickness of the vinyl acetalcopolymer layer is 0.005 to 0.1 mm, especially 0.01 to 0.03 mm, thoughthe preferred thickness is varied to some extent depending on theintended use or the layer structure or arrangement. Further, if thethickness of the heat-sealable resin is 0.01 to 0.1 mm, especially 0.03to 0.07 mm, satisfactory heat sealability is attained. It is preferredthat the thickness of the heat-resistant resin layer and the thicknessof shock absorbing layer be 0.005 to 0.03 mm and 0.01 to 0.03 mm,respectively.

When the laminate structure of the present invention is shaped into acontainer having the heat-sealable resin layer located on the inside andthe vinyl acetal copolymer layer or heat-resistant layer located on theoutside, the resulting container can be advantageously used as aheat-sealable container. For example, in case of a filmy laminatestructure having an entire thickness of 0.04 to 0.15 mm, especially 0.06to 0.10 mm, a bag-like container or pouch can be formed by piling two ofsuch films and heat-sealing the peripheral portions of the films. Stillfurther, a sheet-like laminate structure having an entire thickness of0.1 to 5 mm, especially 0.2 to 2 mm, may be formed into a flanged cupcontainer by vacuum forming, air pressure forming, compression molding,draw forming or the like.

The present invention will now be described in detail by reference tothe following Examples that by no means limit the scope of theinvention.

In these Examples, the degree of acetalization and infrared absorbanceratio were determined according to the following methods.

(1) DEGREE OF ACETALIZATION (1-A) Product Acetalized with Monoaldehyde:

The acetalized product is decomposed by sulfuric acid and themonoaldehyde is distilled and trapped by steam distillation. Thequantitative analysis of the trapped monoaldehyde is carried outaccording to the sodium sulfite method, and the degree of acetalizationis determined based on the results of the quantitative analysis. Theanalysis procedures are as follows:

About 1 g (l g after absolute drying) of the acetalized product sampleis decomposed in 100 cc of a 25% aqueous solution of sulfuric acid, andsteam distillation is conducted to collect a free aldehyde. When thedistillate is acidic, the distillate is carefully neutralized bytitration using a normal solution of sodium hydroxide. Then, 50 cc of anaqueous solution containing pure sodium sulfite at a concentration of 1mole per liter and 3 drops of a 0.1% alcohol solution of thymolphthaleinas an indicator are charged in an Erlenmeyer flask having a capacity of500 cc and neutralization is carefully carried out with a normalsolution of sulfuric acid until the blue color of the indicatordisappears. The sample solution recovered by distillation trapping andneutralization is added to the charge of the Erlenmeyer flask, and themixture is titered with 0.1 N sulfuric acid until the mixture iscompletely decolored. The amount (p, cc) of the sulfuric acid requiredfor the titration is measured.

The total mole number (a) of the units (A) represented by the followingformula: ##STR9## and the units (B) represented by the followingformula: ##STR10## contained in 1 g of the sample is calculatedaccording to the following equation: ##EQU1##

Supposed that the molecular weight of the monoaldehyde is M and theethylene content of the saponified ethylene-vinyl acetate copolymer is umole %, the mole number v of the vinyl groups in 1 g of the sample isgiven by the following formula: ##EQU2## Accordingly, the acetalizationdegree A is calculated according to the following formula: ##EQU3##(1-B) Product Acetalized with Dialdehyde:

The product acetalized with a dialdehyde includes the units (C)represented by the following formula: ##STR11## and the units (D)represented by the following formula: ##STR12##

In general, hydroxylamine reacts with a free aldehyde group at roomtemperature and it reacts with all the aldehyde groups under boiling.Therefore, both the structures (C) and (D) are separated andquantitatively determined by the hydroxylamine hydrochloride methodaccording to the following procedures.

About 1 g (m g after absolute drying) of the sample and 50 cc of a 1 Naqueous solution of hydroxylamine hydrochloride are charged in anErlenmeyer flask having a capacity of 500 cc, and the charge is allowedto stand still at room temperature a whole day and night to effectreaction. Then, the mixture is filtered, and Bromophenol Blue is addedto the filtrate and the mixture is titered with a 0.1 N aqueous solutionof sodium hydroxide. The difference q (cc) of the amount of the solutionrequired for titration between this test and the blank test isdetermined. The mole number b of the units (C) in 1 g of the sample isgiven by the following formula: ##EQU4##

Then, about 1 g (n g after absolute drying) of the sample, 50 cc of a 1N aqueous solution of hydroxylamine hydrochloride and 50 cc of butanolare charged in another Erlenmeyer flask having a capacity of 500 cc, andthe mixture is heated under reflux for 3 hours. After the reaction, themixture is filtered and Bromophenol Blue is added as an indicator to thefiltrate. Titration is carried out with a 0.1 N aqueous solution ofsodium hydroxide, and the difference r (cc) of the amount of thesolution required for titration between this test and the blank test isdetermined. The mole number d of the units (D) in 1 g of the sample isgiven by the following formula: ##EQU5##

Supposed that the molecular weight of the dialdehyde is N and theethylene content in the saponified ethylenevinyl acetate copolymer is umole %, the mole number w of the vinyl groups in 1 g of the sample isgiven by the following formula: ##EQU6## Accordingly, the degree C ofacetalization to the structure (C) is represented by the followingformula: ##EQU7## and the degree D of acetalization to the structure (D)is represented by the following formula: ##EQU8##

(2) Infrared Absorbance Ratio

When a saponified ethylene-vinyl acetate copolymer is acetalized, somenew absorptions appear in the infrared absorption spectrum of theacetalized product. Most of these new absorptions are owing tovibrations of CH and CH₂, and there is also observed an absorption owingto stretching vibrations of the acetal ring --O--CH(R)--O-- at a wavenumber of 1000-1030 cm⁻¹. When R is H, this absorption appears at 1027cm⁻¹ and this absorption is shifted to the short wave length side when Ris a heavy group. Accordingly, the absorbance of this absorption band isused as the index of the degree of acetalization and the absorbanceratio R is calculated according to the following equation: ##EQU9##wherein D₁ stands for the absorbance of the stretching vibration band ofthe acetal ring and D₂ stands for the absorbance of the CH₂ band at 850cm⁻¹.

The absorbance D₂ is used for correction of the thickness of the film.The intensity of this band is weakened when the degree of acetalizationis excessively enhanced. When the degree of the acetalization is withinthe range specified in the present invention, however, reduction of theintensity of this band is very small.

EXAMPLES 1 TO 4

A saponified ethylene-vinyl acetate copolymer having an ethylene contentof 25.4 mole %, a degree of saponification of 99.2% and an intrinsicviscosity of 0.13 l/g was molten and extruded into a film having athickness of 17μ. This film was treated at a treatment temperature of60° C. for 10 minutes (Example 1) in an aqueous glyoxalizing bath havinga sulfuric acid concentration of 12.5% by weight, a sodium sulfateconcentration of 12.5% by weight and a glyoxal concentration of 5.0% byweight. The treated film was washed with water and dried. In order todetermine the degree of glyoxalization of the treated film, the amountof glyoxal was determined according to the hydroxylamine hydrchloridemethod. It was found that glyoxal was bonded to the saponifiedethylene-vinyl acetate copolymer in either the non-crosslinked form[structure (C)] or the crosslinked form [structure (D)], and that thedegree of glyoxalization to the structure (C) was 1.8%, the degree ofglyoxalization to the structure (D) was 1.1 mole % and the totalglyoxalization degree was 2.9 mole %. When the treated film wassubjected to the infrared absorption spectrum analysis, it was foundthat the shoulder owing to the acetal ring appeared at 1025 cm⁻¹ and theabsorbance ratio (R=D₁₀₂₅ /D₈₅₀) of this band was 1.31, which value washigher than the value of the absorbance ratio of 1.15 of theunacetalized product (Comparative Example 1). The so obtained treatedfilm was colorless and transparent, and when the oxygen gas permeabilityof the film was measured, it was found that the film had an oxygen gaspermeability of 1.2 cc/m² per 24 hours (as measured at a temperature of27° C. and a relative humidity of 60%). When this film was treated for 2hours in boiling water at 100° C., neither blanching nor dissolution wascaused and it was confirmed that the film had a good resistance to hotwater. When this film was then subjected to the retort treatment at 135°C. for 10 minutes, neither blanching nor dissolution was caused.

Treated films were prepared in the same manner as described above exceptthat the time for the treatment in the glyoxalizing bath was changed(Examples 2 to 4). Treatment conditions and obtained results arecollectively shown in Table 1 together with the treatment conditions andobtained results of Example 1.

COMPARATIVE EXAMPLE 1

A saponified ethylene-vinyl acetate copolymer having an ethylene contentof 25.4 mole %, a degree of saponification of 99.2% an an intrinsicviscosity of 0.13 l/g was molten and extruded into a film having athickness of 17μ. In the same manner as described in Example 1, the filmwas dipped in boiling water at 100° C. except that the film was notsubjected to the acetalization treatment. The film was whitened and wasin the semi-dissolved state, and the film was converted to a massbecause of autohesion.

COMPARATIVE EXAMPLE 2

A saponified ethylene-vinyl acetate copolymer having an ethylene contentof 25.4 mole %, a degree of saponification of 99.2% and an intrinsicviscosity of 0.13 l/g was molten and extruded into a film having athickness of 17μ. The film was treated for 5 minutes in the sameglyoxalizing bath as used in Examples 1 to 4, and the treated film waswashed with water and dried. When the degree of glyoxalation wasdetermined according to the hydroxylamine hydrochloride method, it wasfound that the degree of glyoxalation to the non-crosslinked type[structure (C)] was 0.2 mole %, the degree of glyoxalation to thecrosslinked type [structure (D)] was 0.1 mole % and the totalglyoxalation degree was 0.3 mole %. When the treated film was dipped inboiling water at 100° C., the film was whitened and simultaneously,extreme deformation took place. Accordingly, it was confirmed that thehot water resistance of this treated film was insufficient.

COMPARATIVE EXAMPLE 3

A saponified ethylene-vinyl acetate copolymer having an ethylene contentof 25.4 mole %, a degree of saponification of 99.2% and an intrinsicviscosity of 0.13 l/g was molten and extruded into a film having athickness of 17μ. The resulting film was treated for 90 minutes in thesame glyoxalizing bath as used in Examples 1 to 4, and the treated filmwas washed with water and dried. When the degree of glyoxalation of theso obtained treated film was determined according to the hydroxylaminehydrochloride method, it was found that the degree of glyoxalation tothe non-crosslinked type [structure (C)] was 26.8 mole %, the degree ofglyoxalation to the crosslinked type [structure (D)] was 29.6 mole % andthe total glyoxalation degree was 56.4 mole %. The oxygen gaspermeability of the resulting acetalized film was very high and the filmwas brittle. Accordingly, this film was not suitable as a packagingmaterial.

Results obtained in Comparative Examples 1 to 3 are collectively shownin Table 1.

EXAMPLE 5

A saponified ethylene-vinyl acetate copolymer having an ethylene contentof 25.4 mole %, a degree of saponification of 99.2% and an intrinsicviscosity of 0.13 l/g was molten and extruded into a film having athickness of 17μ. The film was treated at a treatment temperature of 60°C. for 15 minutes in an aqueous glyoxalizing bath having a hydrochloricacid concentration of 15.0% by weight and a glyoxal concentration of5.0% by weight. The treated film was washed with water and dried. Whenthe amount of glyoxal was determined according to the hydroxylaminehydrochloride method so as to determine the degree of glyoxalation ofthe resulting film, it was found that glyoxal was bonded to thesaponified ethylene-vinyl acetate copolymer in both the non-crosslinkedform [structure (C)] and the crosslinked form [structure (D)], and thatthe degree of glyoxalation to the structure (C) was 3.1 mole % and thedegree of glyoxalation to the structure (D) was 2.6 mole %. When thefilm was subjected to the infrared absorption spectrum analysis, it wasfound that the shoulder owing to the acetal ring appeared at 1025 cm⁻¹and the absorbance ratio R (D₁₀₂₅ /D₈₅₀) was 1.52. This treated film wascolorless and transparent, and when the oxygen gas permeability wasmeasured, it was found that the film had an oxygen gas permeability of2.4 cc/m² per 24 hours as measured at a temperature of 27° C. and arelative humidity of 0%. When the so treated film was dipped in boilingwater at 100° C. for 2 hours, neither blanching nor dissolution wascaused, and it was confirmed that the film had a good resistance to otwater. When the treated film was subjected to the retort treatment at135° C. for 10 minutes, neither blanching nor dissolution was caused.Obtained results are shown in Table 1.

EXAMPLES 6 TO 8

A saponified ethylene-vinyl acetate copolymer having an ethylene contentof 25.4 mole %, a degree of saponification of 99.2% and an intrinsicviscosity of 0.13 l/g was molten and extruded into a film having athickness of 17μ. The resulting film was treated at a treatmenttemperature of 60° C. for 5 minutes (Example 6) in an aqueousformalizing bath having a sulfuric acid concentration of 12.5% byweight, a sodium sulfate concentration of 12.5% by weight and aformaldehyde concentration of 4.6% by weight. The treated film waswashed with water and dried. When the so obtained film was decomposed bysulfuric acid and subjected to steam distillation, formaldehyde wasdetected in the distillate. When the distillate was collected and thedegree of formalization was determined by quantitative analysis offormaldehyde according to the sodium sulfite method, it was found thatthe degree of formalization of the treated film was 18.4 mole %. Whenthe treated film was subjected to the infrared absorption spectrumanalysis, it was found that an absorption band owing to the acetal ring--O--CH₂ --O-- appeared at 1027 cm⁻¹ and that the absorbance ratio R(D₁₀₂₇ /D₈₅₀) of this band was 3.76, which was higher than theabsorbance ratio value of 1.15 of the untreated film (ComparativeExample 1). The treated film was colorless and transparent and theoxygen gas permeability of the treated film was found to be 2.3 cc/m²per 24 hours as measured at a temperature of 27° C. and a relativehumidity of 0%. When this treated film was dipped in boiling water at100° C. for 2 hours, neither blanching nor dissolution was caused, andit was confirmed that the film had a good resistance to hot water. Whenthe treated film was subjected to the retort treatment at 135° C. for 10minutes, neither blanching or dissolution was caused.

The foregoing procedures were repeated in the same manner except thatthe time for the treatment in the formalizing bath was changed (Examples7 and 8). Treatment conditions and obtained results are shown in Table 1together with those of Example 6.

EXAMPLES 9 AND 10

A saponified ethylene-vinyl acetate copolymer having an ethylene contentof 25.4 mole %, a degree of saponification of 99.2% and an intrinsicviscosity of 0.13 l/g was molten and extruded into a film having athickness of 17μ. The resulting film was treated at 50° C. for 30minutes (Example 9) in an aqueous formalizing bath having a sulfuricacid concentration of 4.8% by weight, a sodium sulfate concentration of9.5% by weight and a formaldehyde concentration of 5.3% by weight. Thetreated film was washed with water and dried. When the resulting samplewas decomposed by sulfuric acid and subjected to steam distillation,formaldehyde was detected in the distillate. When the distillate wascollected and the degree of formalization was determined by quantitativeanalysis of formaldehyde in the distilate according to the sodiumsulfite method, it was found that the degree of formalization was 8.8mole %. When the treated film was subjected to the infrared absorptionspectrum analysis, it was found that a band owing to the acetal ring--O--CH₂ --O-- appeared at 1027 cm⁻¹ and the absorbance ratio R (D₁₀₂₇/D₈₅₀) of this band was 2.43. The treated film was colorless andtransparent, and the oxygen gas permeability of this film was found tobe 0.5 cc/m² per 24 hours as measured at a temperature of 27° C. and arelative humidity of 0%. When this film was treated in boiling water at100° C. for 2 hours, neither blanching nor dissolution was caused. Whenthe film was subjected to the retort treatment at 135° C. for 10minutes, neither blanching nor dissolution took place.

The above procedures were repeated in the same manner except that thetime for the treatment in the formalizing bath was changed to 60 minutes(Example 10). Treatment conditions and obtained results are shown inTable 1 together with those of Example 9.

COMPARATIVE EXAMPLE 4

The same saponified ethylene-vinyl acetate copolymer film as used inExamples 6 to 8 was treated at 60° C. for 45 minutes in the sameformalizing bath as used in Examples 6 to 8, and the treated film waswashed with water and dried. When the degree of formalization of theresulting film was determined according to the sodium sulfite method, itwas found that the degree of formalization was 58.2 mole %. The oxygengas permeability of the film was found to be as high as 152 cc/m² per 24hours as measured at a temperature of 27° C. and a relative humidity of0%.

COMPARATIVE EXAMPLE 5

The same saponified ethylene-vinyl acetate copolymer film as used inExamples 9 and 10 was treated at 50° C. for 10 minutes in the sameformalizing bath as used in Examples 9 and 10, and the treated film waswashed with water and dried. When the degree of formalization of thefilm was determined according to the sodium sulfite method, it was foundthat the degree of formalization was 0.4 mole %. When the resulting filmwas dipped in boiling water at 100° C., the film was whitened andextreme deformation took place. Accordingly, it was confirmed that thehot water resistance of the film was insufficient.

Results obtained in Comparative Examples 4 and 5 are shown in Table 1.

EXAMPLES 11 AND 12

A saponified ethylene-vinyl acetate copolymer having an ethylene contentof 25.4 mole %, a degree of saponification of 99.2% and an intrinsicviscosity of 0.13 l/g was molten and extruded into a film having athickness of 17μ. This film was treated at a treatment temperature of40° C. for 5 minutes (Example 11) in an aqueous acetalizing bath havinga sulfuric acid concentration of 5.0% by weight, a sodium sulfateconcentration of 8.3% by weight and a glutaraldehyde concentration of5.5% by weight. The treated film was washed with water and dried. Inorder to determine the degree of acetalization of the treated film byglutaraldehyde, the amount of glutaraldehyde was determined according tothe hydroxylamine hydrochloride method. It was found that glutaraldehydewas bonded to the saponified ethylene-vinyl acetate copolymer in eitherthe noncrosslinked from [structure (C)] or the crosslinked form[structure (D)] though the lather form was predominant, and that thedegree of acetalization to the structure (C) was 0.3%, the degree ofacetalization to the structure (D) was 3.5 mole % and the totalacetalization degree was 3.8 mole %. When the treated film was subjectedto the infrared absorption spectrum analysis, it was found that theshoulder owing to the acetal ring appeared at 1025 cm⁻¹ and theabsorbance ratio (R=D₁₀₂₅ /D₈₅₀) of this band was 1.30, which value washigher than the value of the absorbance ratio of 1.15 of theunacetalized product (Comparative Example 1). The so obtained treatedfilm was colorless and transparent, and when the oxygen gas permeabilityof the film was measured, it was found that the film had an oxygen gaspermeability of 0.7 cc/m² per 24 hours (as measured at a temperature of27° C. and a relative humidity of 0%). When this film was treated for 2hours in boiling water at 100° C., neither blanching nor dissolution wascaused and it was confirmed that the film had a good resistance to hotwater. When this film was then subjected to the retort treatment at 135°C. for 10 minutes, neither blanching nor dissolution was caused.

A treated film was prepared in the same manner as described above exceptthat the time for the treatment in the acetalizing bath was changed to10 minutes (Example 12). Treatment conditions and obtained results arecollectively shown in Table 1 together with the treatment conditions andobtained results of Example 11.

COMPARATIVE EXAMPLE 6

A film having a thickness of 17μ, which was prepared from an aqueoussolution of a polyvinyl alcohol having a viscosity average degree ofpolymerization of 1750 and a degree of saponification of 98.5 mole %according to the dry film-forming method, was treated at a treatmenttemperature of 60° C. for 8 minutes in an aqueous formalizing bathhaving a sulfuric acid concentration of 15.0% by weight, a sodiumsulfate concentration of 15.0% by weight and a formaldehydeconcentration of 5.0% by weight, and the treated film was washed withwater and dried. When the degree of formalization in the resulting filmwas determined according to the sodium sulfite method, it was found thatthe degree of formalization was 22.3 mole %. The oxygen gas permeabilityof the film was found to be 2.8 cc/m² per 24 hours as measured at atemperature of 27° C. and a relative humidity of 0%. Accordingly, it wasconfirmed that the gas barrier property of the film was good. However,when the film was dipped in boiling water at 100° C., deformation wasextreme and the film became in the semi-molten state, and it wasconfirmed that the hot water resistance of the film was very poor.Obtained results are shown in Table 1.

COMPARATIVE EXAMPLE 7

The same polyvinyl alcohol film as used in Comparative Example 6 wastreated at 60° C. for 90 minutes in the same formalizing bath as used inComparative Example 6, and the treated film was washed with water anddried. When the degree of formalization of the resulting film wasdetermined according to the sodium sulfite method, it was found that thedegree of formalization was 60.2 mole %. The film was found to beresistant to the dipping treatment in boiling water at 100° C., but theoxygen gas permeability of the film was found to be as high as 63.0cc/m² per 24 hours as measured at a temperature of 27° C. and a relativehumidity of 0% and it was confirmed that the oxygen barrier property ofthe film was poor. Obtained results are shown in FIG. 1.

COMPARATIVE EXAMPLE 8

The same polyvinyl alcohol film as used in Comparative Example 6 wastreated at 60° C. for 60 minutes in an aqueous glyoxalizing bath havinga sulfuric acid concentration of 15.0% by weight, a sodium sulfiteconcentration of 15.0% by weight and a glyoxal concentration of 5.0% byweight, and the treated film was washed with water and dried. When thedegree of glyoxalization was determined according to the hydroxylaminehydrochloride method, it was found that the degree of glyoxalization tothe non-crosslinked structure was 11.4 mole %, the degree ofglyoxalization to the crosslinked structure was 6.2 mole % and the totalglyoxalization degree was 17.8 mole %. The oxygen gas permeability ofthe treated film was found to be as high as 47.5 cc/m² per 24 hours asmeasured at a temperature of 27° C. and a relative humidity of 0%, andit was confirmed that the oxygen barrier property of the film was poor.When the film was dipped in boiling water at 100° C., deformation wasextreme. As a result, it was confirmed that even when the acetalizationis sufficiently advanced, if there are not present olefin units, nosufficient hot water resistance can be obtained. Results obtained inthis Comparative Example are shown in Table 1.

                                      Table 1                                     __________________________________________________________________________                                      Reaction                                    Acetalizing Bath           Concentra-                                                                           Conditions                                  Aldehyde        Acid       tion of                                                                              Tem-   Degree of Acetalization                         Concent-   Concent-                                                                           Sodium Sul-                                                                          pera-  (mole %)                                        ration     ration                                                                             fate   ture                                                                             Time                                                                              Non-cross-                                                                          Cross-                               Kind (wt.%)                                                                             Kind  (wt.%)                                                                             (wt.%) (°C.)                                                                     (min)                                                                             linked                                                                              linked                                                                            Total                      __________________________________________________________________________    Example 1                                                                           glyoxal                                                                            5.0  sulfuric                                                                            12.5 12.5   60 10   1.8  1.1  2.9                                       acid                                                          Example 2                                                                            "   5.0  sulfuric                                                                            12.5 12.5   60 15   2.9  1.6  4.5                                       acid                                                          Example 3                                                                            "   5.0  sulfuric                                                                            12.5 12.5   60 20   4.4  2.7  7.1                                       acid                                                          Example 4                                                                            "   5.0  sulfuric                                                                            12.5 12.5   60 30   4.8  2.9  7.7                                       acid                                                          Example 5                                                                            "   5.0  hydrochlo-                                                                          15.0 --     60 15   3.1  2.6  5.7                                       ric acid                                                      Example 6                                                                           formalde-                                                                          4.6  sulfuric                                                                            12.5 12.5   60  5  18.4  --  18.4                             hyde      acid                                                          Example 7                                                                           formalde-                                                                          4.6  sulfuric                                                                            12.5 12.5   60 10  27.8  --  27.8                             hyde      acid                                                          Example 8                                                                           formalde-                                                                          4.6  sulfuric                                                                            12.5 12.5   60 15  33.9  --  33.9                             hyde      acid                                                          Example 9                                                                           formalde-                                                                          5.3  sulfuric                                                                             4.8  9.5   50 30   8.8  --   8.8                             hyde      acid                                                          Example 10                                                                          formalde-                                                                          5.3  sulfuric                                                                             4.8  9.5   50 60  16.2  --  16.2                             hyde      acid                                                          Example 11                                                                          glutaral-                                                                          5.5  sulfuric                                                                             5.0  8.3   40  5   0.3  3.5  3.8                             dehyde    acid                                                          Example 12                                                                          glutaral-                                                                          5.5  sulfuric                                                                             5.0  8.3   40 10   0.3  6.4  6.7                             dehyde    acid                                                          Comparative                                                                          --  --   --    --   --     -- --  --    --  --                         Example 1                                                                     Example 2                                                                           glyoxal                                                                            5.0  sulfuric                                                                            12.5 12.5   60  5   0.2  0.1  0.3                                       acid                                                          Example 3                                                                            "   5.0  sulfuric                                                                            12.5 12.5   60 90  26.8  29.6                                                                              56.4                                       acid                                                          Example 4                                                                           formal-                                                                            4.6  sulfuric                                                                            12.5 12.5   60 45  58.2  --  58.2                             dehyde    acid                                                          Example 5                                                                           formal-                                                                            5.3  sulfuric                                                                             4.8  9.5   50 10   0.4  --   0.4                             dehyde    acid                                                          Example 6                                                                           formal-                                                                            5.0  sulfuric                                                                            15.0 15.0   60  8  22.3  --  22.3                             dehyde    acid                                                          Example 7                                                                           formal-                                                                            5.0  sulfuric                                                                            15.0 15.0   60 90  60.2  --  60.2                             dehyde    acid                                                          Example 8                                                                           glyoxal                                                                            5.0  sulfuric                                                                            15.0 15.0   60 60  11.4  6.2 17.8                                       acid                                                          __________________________________________________________________________                  Oxygen Gas      Hot Water Resistance                            Infrared      Permeability                                                                           Rupture                                                                              100° C., 120 min.                                                                    135° C., 10 min.                 Absorbance                                                                            (cc/m.sup.2 per                                                                        Stress blanch-                                                                              disso- blanch-                                                                            disso-                             Ratio R 24 hours)                                                                              (kg/cm.sup.2)                                                                        ing    lution ing  lution                       __________________________________________________________________________    Example 1                                                                           1.31    1.2*     764    not    not    not  not                          Example 2                                                                           1.37    1.3*     767    not    not    not  not                          Example 3                                                                           1.78    1.5*     838    not    not    not  not                          Example 4                                                                           1.95    2.1*     696    not    not    not  not                          Example 5                                                                           1.52    2.4**    775    not    not    not  not                          Example 6                                                                           3.76    2.3**    782    not    not    not  not                          Example 7                                                                           4.52    3.6**    769    not    not    not  not                          Example 8                                                                           5.28    4.7**    771    not    not    not  not                          Example 9                                                                           2.43    0.5**    753    not    not    not  not                          Example 10                                                                          3.38    0.8**    746    not    not    not  not                          Example 11                                                                          1.30    0.7**    738    not    not    not  not                          Example 12                                                                          1.49    0.8**    723    not    not    not  not                          Comparative                                                                         1.15    1.2*     701    obser- obser- obser-                                                                             obser-                       Example 1                     ved    ved    ved  ved                          Example 2                                                                           1.18    1.2*     769    observed                                                                             not    observed                                                                           observed                     Example 3                                                                           3.86    52.0*    180    --     --     --   --                           Example 4                                                                           9.65    152.0**  376    not    not    not  not                          Example 5                                                                           1.72    1.8**    773    observed                                                                             not    observed                                                                           observed                     Example 6                                                                           --      2.8**    --     observed                                                                             observed                                                                             observed                                                                           observed                     Example 7                                                                           --      63.0**   --     not    not    not  not                          Example 8                                                                           --      47.5**   --     observed                                                                             not    observed                                                                           observed                     __________________________________________________________________________     Notes                                                                         1 The oxygen gas permeability was measured according to the equal pressur     method using an oxygen electrode.                                             2 Oxygen gas permeability measuring conditions:                               *at 27° C. and 60% RH                                                  **at 27° C. and 0% RH                                             

EXAMPLES 13 TO 16

A biaxially stretched polyester film having a thickness of 12μ wasbonded to one surface of the treated film obtained in Example 1 by usinga urethane type adhesive, and an unstretched polypropylene film having athickness of 50μ was bonded on the other surface of the treated filmobtained in Example 1 by using the same urethane type adhesive. Theobtained three-layer laminated film was colorless and transparent andthe oxygen gas permeability was found to be 2.4 cc/m² per 24 hours asmeasured at a temperature of 27° C. and a relative humidity of 0%. Whenthis three-layer laminated film was subjected to the retort treatment at135° C. for 10 minutes, occurrence of blanching, wrinkling, contractionor interlaminar peeling was not observed at all. The oxygen gaspermeability of the retorted laminated film was found to be 2.1 cc/m²per 24 hours as measured at a temperature of 27° C. and a relativehumidity of 0%. Thus, it was confirmed that this three-layer laminatedfilm was very excellent as a packaging material to be subjected to heatsterilization.

In the same manner as described above, a biaxially stretched polyesterfilm having a thickness of 12μ and an unstretched polypropylene filmhaving a thickness of 50μ were bonded to one surface and the othersurface, respectively, of each of the treated films differing from theabove film of Example 1 in the time for the glyoxalization treatment(namely, the treated films obtained in Examples 2 to 4), and theresulting laminated films were tested in the same manner as describedabove (Examples 14 to 16). Treatment conditions and obtained results ofthese Examples are collectively shown in Table 2 together with those ofthe abovementioned Example 13.

COMPARATIVE EXAMPLE 9

In the same manner as described in Example 13, a biaxially stretchedpolyester film having a thickness of 12μ and an unstretchedpolypropylene film having a thickness of 50μ were laminated on theunacetalized film obtained in Comparative Example 1 by using a urethanetype adhesive. When the resulting three-layer laminated film wassubjected to the retort treatment, blanching and wrinkling wereconspicuous and peeling was observed in the laminated interfaces.

COMPARATIVE EXAMPLE 10

In the same manner as described in Example 13, a biaxially stretchedpolyester film having a thickness of 12μ and an unstretchedpolypropylene film having a thickness of 50μ were laminated on onesurface and the other surface, respectively, of the treated filmobtained in Comparative Example 2 by using a urethane type adhesive.When the obtained three-layer laiminated film was subjected to theretort treatment at 135° C. for 10 minutes, conspicuous blanching wascaused. Accordingly, it was confirmed that when the degree ofglyoxalization is low, the resulting laminate structure is not suitableas a packaging material to be subjected to heat sterilization.

COMPARATIVE EXAMPLE 11

A three-layer laminated film was obtained by bonding a biaxiallystretched polyester film having a thickness of 12μ to one surface of thetreated film obtained in Comparative Example 3 and an unstretchedpolypropylene film having a thickness of 50μ to the other surface ofsaid treated film by using a urethane type adhesive. The oxygen gaspermeability of the resulting three-layer laminated film was found to beas high as 73 cc/m² per 24 hours as measured at a temperature of 27° C.and a relative humidity of 0%. When the three-layer laminated film wassubjected to the retort treatment at 135° C. for 10 minutes, cracks wereformed in the intermediate layer of the laminated film. Accordingly, itwas confirmed that this laminated film was not suitable as a packagingmaterial to be subjected to heat sterilization.

Results obtained in Comparative Examples 9 to 11 are collectively shownin Table 2.

EXAMPLE 17

A biaxially stretched polyester film having a thickness of 12μ and anunstretched polypropylene film having a thickness of 50μ were bonded toone surface and the other surface, respectively, of the treated filmobtained in Example 5 by using a urethane type adhesive. The oxygen gaspermeability of the so obtained three-layer laminated film was found tobe 2.2 cc/m² per 24 hours as measured at a temperature of 27° C. and arelative humidity of 0%. When this three-layer laminated film wassubjected to the retort treatment at 135° C. for 10 minutes, occurrenceof blanching, wrinkling, contraction or interlaminar peeling was notobserved in the laminated film. The oxygen gas permeability of theretorted laminated film was found to be 2.0 cc/m² per 24 hours asmeasured at a temperature of 27° C. and a relative humidity of 0%.Accordingly, it was confirmed that this three-layer laminated film wasexcellent as a packaging material to be subjected to heat sterilization.Results obtained in this Example are shown in Table 2.

EXAMPLES 18 TO 20

A biaxially stretched polyester film having a thickness of 12μ and afilm having a thickness of 50μ and being composed of a blend comprising85% by weight of a poly-4-methylpentene-1 resin having a melting pointof 230° C., a specific gravity of 0.84 and a melt index of 25 and 15% byweight of an ethylene-propylene copolymer rubber (EPR) having an averagemolecular weight of 100,000 and a propylene content of 35 mole % werebonded to one surface and the other surface, respectively, of thetreated film obtained in Example 6 by using a urethane type adhesive.The oxygen gas permeability of the so obtained three-layer laminatedfilm was found to be 2.7 cc/m² per 24 hours as measured at a temperatureof 27° C. and a relative humidity of 0%. When this three-layer laminatedfilm was subjected to the retort treatment at 135° C. for 10 minutes,occurrence of blanching, wrinkling, contraction or interlaminar peelingwas not observed in the laminated film.

In the same manner as described above, a biaxially stretched polyesterfilm having a thickness of 12μ and an unstretched polypropylene filmhaving a thickness of 50μ were bonded to one surface and the othersurface, respectively, of each of the treated films differing from theabove treated film in the formalizing treatment time (namely, thetreated films obtained in Examples 7 and 8), and the resulting laminatedfilms were tested in the same manner as described above (Examples 19 and20). Treatment conditions and obtained results of these Examples 19 and20 are shown in Table 2 together with those of the above-mentionedExample 18.

EXAMPLES 21 AND 22

A biaxially stretched nylon-6 film having a thickness of 15μ and a filmhaving a thickness of 50μ and being composed of a blend comprising 95%by weight of a polypropylene having a melting point of 163° C. and adensity of 0.90 and 5% by weight of an ethylene-propylene copolymerrubber (EPR) having an average molecular weight of 100,000 and apropylene content of 35 mole % were bonded to one surface and the othersurface, respectively, of the treated film obtained in Example 9 byusing a urethane type adhesive. The so obtained three-layer laminatedfilm was very tough, and the oxygen gas permeability of this three-layerlaminated film was found to be 0.8 cc/m² per 24 hours as measured at atemperature of 27° C. and a relative humidity of 0%. When thisthree-layer laminated film was subjected to the retort treatment at 135°C. for 10 minutes, occurrence of blanching, wrinkling, contraction orinterlaminar peeling was not observed in the laminated film. Obtainedresults of this Example 21 are shown in Table 2.

A biaxially stretched polyester film having a thickness of 12μ and anunstretched nylon-12 film having a thickness of 40μ were bonded to onesurface and the other surface, respectively, of the treated filmobtained in the same manner as in case of the above treated film exceptthat the acetalizing treatment time was changed to 60 minutes (namely,the treated film obtained in Example 10) by using a urethane typeadhesive. This three-layer laminated film was tested in the same manneras described above. Treatment conditions and obtained results of thisExample 22 are shown in Table 2.

COMPARATIVE EXAMPLE 12

A biaxially stretched polyester film having a thickness of 12μ and anunstretched polypropylene film having a thickness of 50μ were bonded toone surface and the other surface, respectively, of the film obtained inComparative Example 4 by using a urethane type adhesive. The oxygen gaspermeability of the so obtained three-layer laminated film was found tobe as high as 148 cc/m² per 24 hours as measured at a temperature of 27°C. and a relative humidity of 0%.

COMPARATIVE EXAMPLE 13

A biaxially stretched polyester film having a thickness of 12μ and anunstretched polypropylene film having a thickness of 50μ were bonded toone surface and the other surface, respectively, of the film obtained inComparative Example 5 by using a urethane type adhesive. When the soobtained three-layer laminated film was subjected to the retorttreatment at 135° C. for 10 minutes, occurrence of conspicuous blanchingwas observed. Thus, it was confirmed that when the degree offormalization is low, the resulting laminate film structure is notsuitable as a packaging material to be subjected to heat sterilization.

Results obtained in Comparative Examples 12 and 13 are shown in Table 2.

EXAMPLES 23 and 24

A biaxially stretched polyester film having a thickness of 12μ and afilm having a thickness of 50μ and being composed of anethylene-propylene block copolymer resin having a melting point of 160°C., a density of 0.90 and an ethylene content of 5 mole % were bonded toone surface and the other surface, respectively, of the treated filmobtained in Example 11 by using a urethane type adhesive. The oxygen gaspermeability of the so obtained three-layer laminated film was found tobe 1.2 cc/m² per 24 hours as measured at a temperature of 27° C. and arelative humidity of 0%. When this three-layer laminated film wassubjected to the retort treatment at 135° C. for 10 minutes, occurrenceof blanching, wrinkling, contraction or interlaminar peeling was notobserved (Example 23).

A biaxially stretched polyester film having a thickness of 12μ and afilm having a thickness of 50μ and being composed of anethylene-propylene block copolymer having a melting point of 160° C., adensity of 0.90 and an ethylene content of 5 mole % were bonded to onesurface and the other surface, respectively, of the treated filmobtained in Example 12 (the acetalization treatment time being 10minutes) by using a urethane type adhesive. The oxygen gas permeabilityof the so obtained three-layer laminated film was found to be 1.7 cc/m²per 24 hours as measured at a temperature of 27° C. and a relativehumidity of 0%. When this three-layer laminated film was subjected tothe retort treatment at 135° C. for 10 minutes, occurrence of blanching,wrinkling, contraction or interlaminar peeling was not observed (Example24).

Results obtained in Examples 23 and 24 are shown in Table 2.

COMPARATIVE EXAMPLE 14

A biaxially stretched polyester film having a thickness of 12μ and anunstretched polypropylene film having a thickness of 50μ were bonded toone surface and the other surface, respectively, of the film obtained inComparative Example 6 by using a urethane type adhesive. The oxygen gaspermeability of the resulting three-layer laminated film was found to be2.9 cc/m² per 24 hours as measured at a temperature of 27° C. and arelative humidity of 0%, and it was confirmed that the oxygen gasbarrier property of this laminated film was good. However, when thelaminated film was subjected to the retort treatment at 135° C. for 10minutes, occurrence of conspicuous blanching and interlaminar peelingwas observed, and it was confirmed that the adoptability of thelaminated film to the retort treatment was poor.

Obtained results are shown in Table 2.

COMPARATIVE EXAMPLE 15

A biaxially stretched polyester film having a thickness of 12μ and anunstretched polypropylene film having a thickness of 50μ were bonded toone surface and the other surface, respectively, of the film obtained inComparative Example 7 by using a urethane type adhesive. When thisthree-layer laminated film was subjected to the retort treatment at 135°C. for 10 minutes, it was found that the laminated film had a goodadaptability to the retort treatment. However, the oxygen gaspermeability of the laminated film was found to be as high as 68.5 cc/m²per 24 hours as measured at a temperature of 27° C. and a relativehumidity of 0%.

Obtained results are shown in Table 2.

COMPARATIVE EXAMPLE 16

A biaxially stretched polyester film having a thickness of 12μ and anunstretched polypropylene film having a thickness of 50μ were bonded toone surface and the other surface, respectively, of the film obtained inComparative Example 8 by using a urethane type adhesive. The oxygen gaspermeability of the resulting three-layer laminated film was found to be49.7 cc/m² per 24 hours as measured at a temperature of 27° C. and arelative humidity of 0%, and it was confirmed that the oxygen gasbarrier property of this laminated film was poor. When this laminatedfilm was subjected to the retort treatment at 135° C. for 10 minutes,occurrence of blanching and interlaminar peeling was observed.Accordingly, it was confirmed that even when the acetalization issufficiently advanced, if there are not present olefin units, asufficient adaptability to the retort treatment cannot be obtained.

Obtained results are shown in Table 2.

                                      Table 2                                     __________________________________________________________________________    Acetalizing Bath         Sodium                                                                             Reaction  Degree of Acetalization               Aldehyde        Acid     Sulfate                                                                            Conditions                                                                             (mole %)                                          Concen-  Concen-                                                                            Concen-                                                                            Tempe-   non-                                              tration  tration                                                                            tration                                                                            rature                                                                            Time cross-                                                                             cross-                                  Kind (wt. %)                                                                            Kind                                                                              (wt. %)                                                                            (wt. %)                                                                            (°C.)                                                                      (min)                                                                              linked                                                                             linked                                                                            Total                         __________________________________________________________________________    Example 13                                                                          glyoxal                                                                            5.0  sulfuric                                                                          12.5 12.5 60  10   1.8  1.1 2.9                                           acid                                                          Example 14                                                                          "    5.0  sulfuric                                                                          12.5 12.5 60  15   2.9  1.6 4.5                                           acid                                                          Example 15                                                                          "    5.0  sulfuric                                                                          12.5 12.5 60  20   4.4  2.7 7.1                                           acid                                                          Example 16                                                                          "    5.0  sulfuric                                                                          12.5 12.5 60  30   4.8  2.9 7.7                                           acid                                                          Example 17                                                                          "    5.0  hydro-                                                                            15.0 --   60  15   3.1  2.6 5.7                                           chloric                                                                       acid                                                          Example 18                                                                          formalde-                                                                          4.6  sulfuric                                                                          12.5 12.5 60  5    18.4 --  18.4                                hyde      acid                                                          Example 19                                                                          formalde-                                                                          4.6  sulfuric                                                                          12.5 12.5 60  10   27.8 --  27.8                                hyde      acid                                                          Example 20                                                                          formalde-                                                                          4.6  sulfuric                                                                          12.5 12.5 60  15   33.9 --  33.9                                hyde      acid                                                          Example 21                                                                          formalde-                                                                          5.3  sulfuric                                                                          4.8   9.5 50  30   8.8  --  8.8                                 hyde      acid                                                          Example 22                                                                          formalde-                                                                          5.3  sulfuric                                                                          4.8   9.5 50  60   16.2 --  16.2                                hyde      acid                                                          Example 23                                                                          glutar-                                                                            5.5  sulfuric                                                                          5.0   8.3 40  5    0.3  3.5 3.8                                 aldehyde  acid                                                          Example 24                                                                          glutar-                                                                            5.5  sulfuric                                                                          5.0   8.3 40  10   0.3  6.4 6.7                                 aldehyde  acid                                                          __________________________________________________________________________                Oxygen Gas Permeability                                                       (cc/m.sup.2 per 24 hours)                                                                            Adaptability to Retorting                        Infrared                                                                            Layer        after retort-                                                                           (135° C., 10 minutes)                     Absorbance                                                                          Laminate                                                                              before                                                                             ing (135° C.,                                                                    blanch-                                          Ratio (R)                                                                           Structure                                                                             retorting                                                                          10 minutes)                                                                             ing    wrinkling                                                                             peeling                     __________________________________________________________________________    Example 13                                                                          1.31  12X17E* 50Q                                                                           2.4  2.1       not    not     not                         Example 14                                                                          1.37  12X17E* 50Q                                                                           2.6  2.8       not    not     not                         Example 15                                                                          1.78  12X17E* 50Q                                                                           2.5  2.7       not    not     not                         Example 16                                                                          1.95  12X17E* 50Q                                                                           3.2  3.5       not    not     not                         Example 17                                                                          1.52  12X17E* 50Q                                                                           2.2  2.0       not    not     not                         Example 18                                                                          3.76  12X17E* 50M*                                                                          2.7  1.4       not    not     not                         Example 19                                                                          4.52  12X17E* 50Q                                                                           3.4  4.4       not    not     not                         Example 20                                                                          5.28  12X17E* 50Q                                                                           4.3  4.4       not    not     not                         Example 21                                                                          2.43  15N17E*50Q*                                                                           0.8  1.6       not    not     not                         Example 22                                                                          3.38  12X17E*40N'                                                                           2.9  2.5       not    not     not                         Example 23                                                                          1.30  12X17E* 50Q                                                                           1.2  0.8       not    not     not                         Example 24                                                                          1.49  12X17E* 50Q                                                                           1.7  0.6       not    not     not                         __________________________________________________________________________                             Sodium                                                                             Reaction Degree of Acetalization                Aldehyde        Acid     Sulfate                                                                            Conditions                                                                             (mole %)                                          Concen-  Concen-                                                                            Concen-                                                                            Tempe-   non-                                              tration  tration                                                                            tration                                                                            rature                                                                            Time cross-                                                                             cross-                                  Kind (wt. %)                                                                            Kind                                                                              (wt. %)                                                                            (wt. %)                                                                            (°C.)                                                                      (min)                                                                              linked                                                                             linked                                                                            Total                         __________________________________________________________________________    Comparative                                                                         --   --   --  --   --   --  --   --   --  --                            Example 9                                                                     Comparative                                                                         glyoxal                                                                            5.0  sulfuric                                                                          12.5 12.5 60   5    0.2 0.1  0.3                          Example 10      acid                                                          Comparative                                                                         "    5.0  sulfuric                                                                          12.5 12.5 60  90   26.8 29.6                                                                              56.4                          Example 11      acid                                                          Comparative                                                                         formal-                                                                            4.6  sulfuric                                                                          12.5 12.5 60  45   58.2 --  58.2                          Example 12                                                                          dehyde    acid                                                          Comparative                                                                         formal-                                                                            5.3  sulfuric                                                                           4.8  9.5 50  10    0.4 --   0.4                          Example 13                                                                          dehyde    acid                                                          Comparative                                                                         formal-                                                                            5.0  sulfuric                                                                          15.0 15.0 60   8   22.3 --  22.3                          Example 14                                                                          dehyde    acid                                                          Comparative                                                                         formal-                                                                            5.0  sulfuric                                                                          15.0 15.0 60  90   60.2 --  60.2                          Example 15                                                                          dehyde    acid                                                          Comparative                                                                         glyoxal                                                                            5.0  sulfuric                                                                          15.0 15.0 60  60   11.4 6.2 17.8                          Example 16      acid                                                          __________________________________________________________________________                        Oxygen Gas Permeability                                                                      Adaptability to Retorting                                      (cc/m.sup.2 per 24 hours)                                                                    (135° C., 10 minutes)                     Infrared            after retort-                                             Absorbance                                                                          Layer Laminate                                                                        before                                                                              ing (135° C.,                                                                   blanch-                                          Ratio (R)                                                                           Structure                                                                             retorting                                                                           10 minutes)                                                                            ing    wrinkling                                                                           peeling                       __________________________________________________________________________    Comparative                                                                         1.15  12X17E 50Q                                                                            1.8   --       observed                                                                             observed                                                                            observed                      Example 9                                                                     Comparative                                                                         1.18  12X17E*50Q                                                                            1.9   --       observed                                                                             observed                                                                            observed                      Example 10                                                                    Comparative                                                                         3.86  12X17E*50Q                                                                            73.0  --       --     --    --                            Example 11                                                                    Comparative                                                                         9.65  12X17E*50Q                                                                            148.0 --       --     --    --                            Example 12                                                                    Comparative                                                                         1.72  12X17E*50Q                                                                            0.7   --       observed                                                                             observed                                                                            observed                      Example 13                                                                    Comparative                                                                         --    12X17E*50Q                                                                            2.9   --       observed                                                                             observed                                                                            observed                      Example 14                                                                    Comparative                                                                         --    12X17E*50Q                                                                            68.5  96.3     not    not   not                           Example 15                                                                    Comparative                                                                         --    12X17E*50Q                                                                            49.7  --       observed                                                                             observed                                                                            observed                      Example 16                                                                    __________________________________________________________________________     Notes                                                                         1 The oxygen gas permeability was measured at a temperature of 27°     C. and a relative humidity of 0% according to the equal pressure method       using an oxygen electrode.                                                    2 Symbols in the layer laminate structure have the following meaning:         12X: polyester film having a thickness of                                     17E: unacetalized saponified ethylenevinyl acetate copolymer film having      thickness of 17                                                               17E*: acetalized saponified ethylenevinyl acetate copolymer film having a     thickness of 17                                                               50Q: polypropylene film having a thickness of                                 50Q*: polypropyleneEPR blend film having a thickness of                       50M*: poly4-methylpentene-1-EPR blend film having a thickness of              15N: nylon6 film having a thickness of                                        40N': nylon12 film having a thickness of 40μ.                         

What is claimed is as my invention:
 1. A packaging film material havingexcellent hot water resistance and excellent oxygen barrier property incombination, which consists essentially of an olefinvinyl alcohol-vinylacetal copolymer consisting essentially of 20 to 40 mole % of olefinunits and 80 to 60 mole % of vinyl units, 50 to 98 mole % of the vinylunits being vinyl alcohol units and 2 to 50 mole % of the vinyl unitsbeing at least one kind of vinyl acetal units selected from the groupconsisting of (A) units represented by the following formula: ##STR13##wherein R₁ stands for a hydrogen atom or a molovalent aliphatic,aromatic or aliphatic-aromatic group,(B) units represented by thefollowing formula: ##STR14## wherein R₁ is as defined above, (C) unitsrepresented by the following formula: ##STR15## wherein R₂ stands for adirect bond or a divalent aliphatic, aromatic or aliphatic-aromaticgroup, and (D) units represented by the following formula: ##STR16##wherein R₂ is as defined above.
 2. A packaging film material havingexcellent hot water resistance and excellent oxygen barrier property incombination, which consists essentially of an olefinvinyl alcohol-vinylacetal copolymer consisting essentially of 20 to 40 mole % of olefinunits and 80 to 60 mole % of vinyl units, 50 to 98 mole % of the vinylunits being vinyl alcohol units and 2 to 50 mole % of the vinyl unitsbeing at least one kind of vinyl acetal units selected from the groupconsisting of(C) units represented by the following formula: ##STR17##and (D) units represented by the following formula: ##STR18## the molarratio of non-crosslinked vinyl acetal units (C)/crosslinked vinyl acetalunits (D) being in the range of from 1/0.3 to 1/50.
 3. A packaging filmmaterial according to claim 2 wherein the molar ratio of non-crosslinkedvinyl acetal units (C)/crosslinked vinyl acetal units (D) is in therange of from 1/0.5 to 1/30.